Long term objective of this research is the quantitative description of the placental exchange of metabolites between mother and fetus. In the next three years our attention will be focused in the regulation of maternal placental blood flow and the uptake of substrates by the pregnant uterus. The experiments will be on nonanesthetized, unstressed sheep with indwelling catheters in the left ventricle, the femoral arteries, the uterine veins and the amniotic cavity. The studies on circulation will utilize electromagnetic flow probes around both uterine arteries and the determination of regional blood flows with a radioactive microsphere technique. The normal growth of placental blood flow will be described and related to placental growth. The effect of estrogens and catecholamines on placental blood flow will be determined. The uterine uptakes of O2, glucose and short chain fatty acids in normal and starved ewes will be measured throughout gestation.